The science behind Guppy Guppy Evolution

It turns out the humble guppy has a lot to teach us about evolution.



A small fish with a big story to tell

They may be tiny but Trinidadian guppies are the rockstars of evolutionary science.  They live in steep mountain streams that flow across many waterfalls before they reach the ocean. These waterfalls are important barriers, keeping predators out of parts of the stream. Guppies that live above the waterfalls have few predators to contend with while the guppies below….well, they’ve got to stay vigilant in order to survive and reproduce. This means that guppies living in the same stream can experience very different challenges for survival. Some have it easy, while others are likely to be lunch.

So what does this have to do with evolution?















It started with an puzzling observation by a biologist named John Endler. Working along these streams, Endler noticed the guppies had a wide range of coloring. Some guppies had vivid colors and large spots, while others were relatively drab and colorless. Being a scientist, Endler did what scientists do when they make an observation they can’t explain – he devised an experiment to understand why these guppies were so different. Endler moved guppies from below waterfalls were there were lots of predators to places above the waterfalls where there were no or few predators and waited for many months. When he came back he discovered that the guppies in places without predators had significantly more color than the guppies below waterfalls where all the predators were. He was on his way to showing that male guppy color patterns evolve as a trade-off between attracting females and avoiding predators.

But there was more to learn from the guppy.

David Reznick, an evolutionary biologist from University of California Riverside, saw an opportunity to use the streams in Trinidad as “giant test tubes” to learn more about how evolution works. Like Endler before him, Reznick moved the guppies from below and above waterfalls and through his experiments learned that guppies can adapt to the predators in their new environment within 30-60 generations (about 11 years). That means animals could evolve at breakneck speeds – much faster than what we could tell from the fossil record!

How did he find this out?










Reznick transplanted guppies from one part of the stream where predatory pike cichlids prey on adult guppies and moved them above waterfalls where a different predator – a killifish – preyed on babies guppies but left adult guppies alone.  Over time, the guppies in places where pike cichlids ate adults evolved to have as many babies as possible earlier in their lifetimes. Guppies in places where killifish ate babies evolved in an opposite way – they had fewer, larger babies later in life. It’s a simple experiment but showed that evolution could occur much faster than was previously thought. Now, we could watch evolution occur in a fish population in a matter of years.

Want to learn more about what guppies have taught us about evolution? Check out Reznick’s guppy website.


See photos of scientists in action >